Furnaces and ovens for heating articles at elevated temperatures are generally not precise, nor quick to respond to temperature changes. Furnace systems generally have a high degree of inertia, wherein the heating elements and temperature monitors respond very slowly to external commands. Heating systems therefore tend to be difficult to control and temperature requirements can rarely be held to exacting tolerances.
In recent years the need to control furnace temperatures to precise and demanding tolerances has become more critical, particularly in the manufacture of semiconductor materials. Such materials generally require prolonged cycles of heating or cooling at precisely held temperatures or temperature gradients in order that homogeneous, low-defect crystals can be achieved.
It is impractical to have human monitoring of such prolonged heating and cooling cycles so that greater dependence is made upon automated furnaces.
As a precaution to a malfunctioning furnace, a temperature detector may be installed to detect a temperature condition in the furnace that exceeds a safe amount, thereby causing the generation of an alarm so that personnel can shut down the furnace; or the detector may cause automatic shut down of the furnace. As will be appreciated such shut down results in a failed effort to complete the cycle and a great deal of time and effort is lost.